1. Field of the Invention
This invention relates to a ball bearing device for the swing arm of a disc driving apparatus for a magnetic disc, an optical disc or the like.
2. Related Background Art
The bearing portion of a ball bearing device for a swing arm according to the prior art, as shown in FIG. 12A of the accompanying drawings, has ball bearings 1 and 11 having grease enclosed therein, and the ball bearings are used under a pre-load at predetermined positions. FIG. 12B of the accompanying drawings shows the surface pressure distribution 14 of the ball bearing 11 in a cross-section taken along the line 12B--12B of FIG. 12A, and the surface pressure distribution 14 is indicated by a circle, and the radial bearing rigidity of all portions in the circumferential direction thereof is constant.
As shown, there are fitting portions on both of the inner diametral surface of the inner race of the ball bearing fitted to a shaft 5 and the outer diametral surface of the outer race fitted to a housing 10.
These fitting portions are adhesively secured to the shaft 5 and the housing 10 over the entire bearing circumference of the ball bearings 1 and 11.
FIG. 12C of the accompanying drawings schematically shows the actually used state of the ball bearing device for a swing arm according to the prior art.
Recently, higher and higher density has been required of magnetic disc apparatuses. Therefore, the width of tracks for recording signals on the disc has become narrower and narrower, and higher speed of access to a target track and higher accuracy of positioning performance have been required of a swing arm carrying a head for recording and reproducing signals.
In order to satisfy the required higher speed and higher accuracy of control, freedom from a torque fluctuation such as a torque spike, a low torque, etc. is required of the ball bearings 1 and 11 supporting the swing arm 9. Also, high stability and low torque of the control of the swing arm system when controlled at a high speed are desired.
Heretofore, in the ball bearing device for the swing arm, as shown in FIG. 12A, the two ball bearings 1 and 11 have been accurately assembled together with a pre-load applied in the axial direction thereof to thereby achieve the higher accuracy of the bearing device. The present invention has as its object to provide a ball bearing device for a swing arm in which the stability of a swing arm system is enhanced and the higher speed and higher accuracy of control are possible.